(1) Field of the Invention
This invention relates to an improved device for dampening vibrational motion.
(2) Description of the Prior Art
It is well known to dampen vibrational motion through the interaction of a plunger and a fluid in an enclosed chamber of a housing. Typically, the plunger is fixed to a moving part, and the housing is fixed to a stationary part, or another moving part. This type of dampening device is used to dampen motion along the axis of the rotary plunger, and has no facility for dampening rotary motion about the axis of the plunger.
The energy which such prior art dampeners can absorb and how quickly energy can be absorbed depends upon parameters such as size of the plunger, viscosity, temperature, aeration, volume and pressure of the fluid. The energy absorption characteristic for a given dampening device historically has been established by selection of an appropriate combination of such parameters.
However, the absorption characteristic is subject to substantial change over time as a result of normal use and wear. Leakage of fluid from the chamber is expected after a period of use, causing certain changes in the fluid volume and pressure, and typically a change in the fluid temperature. Further, such prior art dampeners have limited or no facility for automatic adjustment, while in use, to suit changing conditions. Still further, such devices usually require sufficient space in the direction of the plunger axis for substantial plunger travel in the fluid.
Accordingly, there is a need for a dampening device having a selected energy absorption characteristic which remains stable over time, and having facility for automatic adjustment of the energy absorption characteristic while the device is in operation. Further, there is a need for such a device not requiring fluid for absorption of energy. Further, there is a need for such a device as can absorb motion along the axis of the plunger and rotary motion around the axis of the plunger. Still further, there is a need for dampening devices not requiring lengthy travel of a piston in a cylinder for activation, therefore not requiring undue extent of space along the axis of the plunger.